Radiant heat reflecting device



June 20, 1967 J. P. CLUNE ETAL 3,327,041

RADIANT HEAT REFLECTING DEVICE Filed April 30, 1964 2 Sheets-Sheet 1 FIG.!

JAMES F. CLUNE HAROLD H. HALL JR INVENTORS ATTORNEY J. P. CLUNE ETAL June 20, 1967 RADIANT HEAT REFLECTING DEVICE 2 Sheets-Sheet 2 Filed April 30, 1964 JAMES F? CLUNE HAROLD H. HALL JR.

INVENTORS gnm/ ww ATTORNEY United States Patent 3,327,041 RADHANT HEAT REFLECTING DEVICE James P. (Zlune, Banvers, and Harold H. Hall, lira,

Marblehead, Mass, assignors to ylvania Electric Products line, a corporation of Delaware Filed Apr. 30, 1964, Ser. No. 363,386 Claims. (Cl. 13-20) This invention relates to high temperature furnaces and more particularly to heat shields for such furnaces.

Various heat shielding configurations have been used by the art, however, most of them require elaborate fabricating and maintenance procedures. These heat shield pack units, as they are called in the art, include a number of joined, spaced-apart heat shield leaves. Usually, the leaves are made from a refractory metal such as tungsten, molybdenum, columbium or tantalum.

Heat shields of refractory metals have previously been used for high temperature applications and their ability to withstand high temperatures without appreciable deformation or distortion is well known to the art. An application in which such metals are frequently used is high temperature vacuum furnaces. Such furnaces can attain temperatures in excess of 1500 and often as high as 2500 to 3000 and above. These furnaces, which are heated by electric power, attain such temperatures in a so-called hot zone which is inside a heating element. Because it is necessary to eliminate oxidation insofar as possible, it is essential that the heating operation takes place in an atmosphere free of oxygen and preferably in a vacuum. Usually positioned adjacent to the walls of the furnace and surrounding the heating element is the metal heat shield pack which reflects and radiates outwardly-emanating heat back into the hot zone.

The positioning of these shields frequently is quite critical to prevent furnace wall destruction and to keep heat loss at a minimum. If the heat shield pack shifts during operation of the furnace due to deformation of the fastening devices which hold it in place, rigid temperature control can be quite difl'icult to attain and the individual leaves may be break.

According to the prior art, spacing of these leaves from one another is accomplished by machining numerous alignment holes in the refractory metal and inserting bolts and spacers therein. If one of the leaves broke or tore, every bolt and spacer had to be removed from the heat shield pack before a new leaf could be substituted.

Additionally, the machining of holes in refractory material is a large part of the cost of manufacturing the packs. However, these holes will sometimes spawn cracks or fissures and thereby reduce the life of the device. It is therefore desirable to reduce the manufacturing cost and make the heat shield packs more efficient. Such attainments can be realized with a device having a minimum of holes and in which the individual leaves can be replaced easily if they break.

An object of this invention is to reduce the cost and increase the stability of heat shield packs of high temperature furnaces.

Another object of this invention is to provide a heat shield pack in which an individual heat shield leaf can be readily replaced without disassembling the entire heat shield pack.

These and other objects, features and advantages of the invention will be apparent from the following specification when taken in conjunction with the accompanying drawing in which:

FIGURE 1 is an elevational cross-section of a typical high temperaure furnace, showing in particular the series of heat shield leaves in position in a furnace.

FIGURE 2 is a top plan view of the furnace of FIG- URE 1 taken on the lines 22 of FIGURE 1.

3,327,041 Patented June 20, 1967 And FIGURE 3 is an enlarged detail cross-section of two heat shield leaves showing in particular the typical spacing arrangement between the leaves.

Referring to FIGURE 1, a conventional high temperature furnace is shown wherein an outer tank 10 houses the various components of the furnace. Located within the tank 10 is a cold wall cylinder 12 which is elevated above the floor of the tank by the supports 14. Between the outer tank 10 and the cold wall 12 are three spaced-apart insulated power leads 16, which supply current to a heating element 18 that is supported within the cold wall 12. A bottomless heating element 18 radiates a considerable amount of heat and is separated from the cold wall 12 by the heat shield pack of our invention. This heat shield pack can include generally cyclindrical heat shields 20, opened at either end and enclosing the heating element 18. Fitted to the top opening of cylindrical shields 20 is a cover unit 24 formed of generally flat discs 48. When the cover unit is seated in place, it will enclose the heating element 18 within a cavity 26 formed by cylindrical heat shield 20. The bottom opening of the cylindrical heat shield 20 is closed by a lower closure 27 formed of generally flat spaced-apart discs 56. This arrangement will completely enclose the heating element 18, thereby protecting the cold wall 12 from heat that is radiated by the heating element 18.

Cover unit 24 is made up of several flat discs of refractory metal 48, secured and spaced from one another by a combination of refractory metal nuts and bolts. Two or more of the bolts 50 pass through the discs and the ends of each are provided with nuts 52. The nut and bolt arrangement will be fully described hereinafter. The purpose of the nut and bolt combination is to prevent the discs 48 from being displaced during the operation of the furnace. Alternate discs 48 of the cover unit 24 are pierced for the inclusion of spacers 54, also made of refractory metal. These spacers 54 are similar in construction to the nuts 52 and bolts 50 of the cover unit 24 and their description Will also appear later. The lower two discs 48a of the cover unit 24 are of slightly smaller diameter than the diameter of the innermost leaf of the side shield unit 20. The remaining discs of the cover unit 24 are the same or greater diameter as the outer leaf of the shield unit 20. Hence the top discs will rest on and cover the top edges of the side sheets 22, and this will place the bottom two discs 48a Within the cavity 26 formed by the side sheets 22, thus preventing displacement of the cover during heating.

Lower closure 27 is also made up of spaced-apart refractory metal discs 56, the diameter of each disc 56 being the same as the two lower discs 48a of the cover unit 24. The lower closure discs 56 are secured and spaced apart from one another in the same manner as in the cover unit; that is, with a nut 58, bolt 60 and spacer 62. This lower closure 27 is positioned above the floor of the cold Wall 12 and within the cavity 26 formed by the side sheets 22 thereby protecting the exposed areas of the cold wall. The bolts 60 that secure the discs 56 together on the lower closure 27 are extended above the surface of the uppermost disc of lower closure 27 to provide stanchions 'for supporting a hearth plate 63 made up of three spaced-apart refractory metal discs 64. These discs are similar to the discs 48 and 56, but are smaller in diameter, so that they extend into the interior of the heating element 18 for the purpose of supporting workpieces that are placed Within the heating element 18.

Referring to FIGURE 2, which is a plan view taken on the line 22 of FIGURE 1, the drawing shows in particular, the general shape and arrangement of the cylindrical heat shield leaves 22 located adjacent to the cold wall 12. Each of the heat shield leaves 22 are formed as an open-ended cylinder. The free ends of the leaves are overlapped to compensate for thermal expansion and contraction. The number of heat shield leaves which are used is not critical and can be varied depending on the application. We have found that for most applications six leaves of gradually smaller diameters can be spaced concentrically and equally from one another. A slot 32 disposed in the side leaves 22 is cut for electrical insulation of the arms 34 of heating element 18 from the shield pack. To prevent the individual leaves 22 from becoming disarranged, a nut bolt and spacer assembly 36 is used. We prefer to employ refractory metal hardware that comprises at least two substantially irresilient helically wound refractory metal coils having a pitch of 100 percent or sometimes slightly more (100% is when the turns are touching). One of the helical windings forms what can be called a bolt 38 and the other forms what can be called a nut 40. The thread on the bolt 38 is formed by the external surfaces of the substantially circular convolutions of the latters winding. The diameter of the threads of the bolt 38 is preferably just slightly les than the internal diameter of the nut 4, thereby allowing easy screw-type insertion and removal. It can be mentioned at this time that preferably only two bolts 38 are used to secure the shield pack to the walls. These bolts pass through aligned holes in the heat shield leaves 22 and also through aligned holes in the cold Wall 12. A nut 40 of helical winding can be screwed upon each end of the bolt 38 thereby securing the bolts and thus preventing the heat shield pack 20 from rotation.

The heat shield leaves 22 as mentioned above are overlapped at their extremities and it is therefore necessary to space them from one another. Such spacing is accomplished with nuts and bolts such as previously described. According to our arrangement, holes are drilled in every other leaf of the pack. A spacer formed of a nut and bolt is disposed in each hole and screwed tightly in place with the nut firmly disposed against the leaf. The distal ends of each of the spacers abuts against an ad acent leaf thereby equally separating them from one another.

As sectional detail of three seen in FIGURE 3 which is an enlarged crossof the heat shield leaves, a short bolt 42 made of convolutions of refractory metal wire as described above is inserted in a hole 46 in a leaf 22.-A pair of nuts 44 similar to nuts 40 are turned on the bolt 42. This operation is performed prior to inserting the individual leaves in place within the furnace. The length of the nut 44 can equal the spacing required between the heat shield leaves 22. u

The assembly of the heat shield pack disclosed above is readily performed by inserting nut and bolt spacers at various locations on alternate heat shield leaves 22. Thereafter each leaf 22 is positioned within the cold wall 12, placing the innermost leaf and then successively fitting larger diameter leaves in position until the required number is attained. The holes of the heat shield leaves are then aligned by placing the elongated bolts 38 through the aligned holes of the sheets 22 and also through the co-operating holes in the cold wall 12. Nuts 40 are then placed on either end of the bolts 38, thereby securing the leaves in place. 1

The lower closure 27 is also assembled prior to installation within the cold wall, by nuts and bolts such as described above, with the exception that the bolts 58 will extend above the uppermost discs. The lower closure 27 is placed in cavity 26 so that the hearth plate 63 can be disposed on the upstanding bolts 60.

Heating element 18 is then placed into the cavity 26, formed by the heat shield 20. The arms 34 of heating element 18 will extend through the aligned slots 32 and the mating slots provided in the cold wall and connected and supported to the upstanding insulated power leads 16. Assembly of the cover unit 24 is performed before it is placed in the furnace using thee nut and bolt construction mentioned above.

It i apparent that modifications and changes canbe made Within the spirit and scope of the instant invention but it is our intention however, to be limited only by the spirit and scope of the following claims.

As our invention we claim:

1. A heat shield pack comprising: at least a first outer, a second intermediate and a third inner concentrically disposed refractory metal heat shield leaves; at least three aperture means disposed on said intermediate heat shield leaf; means disposed and attached to said second intermediate leaf in each of said apertures for separating the intermediate leaf from said first outer leaf and the third inner leaf, the distal ends of each of said separating means abutting against but not attached to said first outer and said third inner said leaves.

2. A heat shield pack according to claim 1 further including a cover plate of at least three heat shield discs of refractory metal; means forming at least one aperture disposed on the intermediate of said heat shield discs, means disposed and attached to said intermediate leaf in said aperture for separating the apertured discs from the other two of said heat shield discs, the distal ends of said separating means abutting against the other two of said discs, at least one of said heat shield discs having a smaller diameter than the other two discs.

3. A heat shield pack according to claim 1 further including a lower closure of at least three heat shield discs of a refractory metal, means forming at least one aperture disposed on the intermediate of said heat shield discs, means disposed and attached in the aperture of said intermediate disc for separating it from the other two of said discs, the distal ends of said separating means abutting against the other two of said discs, each of said heat shield discs having at least three aligned apertures; at least three bolts of refractory metal extending through said aligned apertures and above the top of said discs.

4. A heat shield pack according to claim 1, further including means forming at least two more apertures in each of said leaves, each of these apertures being aligned with a corresponding aperture in an adjacent leaf; tie means comprising nuts and bolts formed of helical convolutions of refractory metal wire disposed in the aligned apertures; said nuts being disposed on the end of each of said bolts, thereby preventing rotation of the leaves of said heat shield pack.

5. A heat shield comprising: at least three refractory metal heat shield leaves; at least one aperture disposed in the intermediate heat shield leaf; means for separating the outer heat shield leaves from the intermediate leaf, said means comprising a substantial irresilient convolution of a refractory metal wire extending on both sides of said intermediate leaf; a pair of substantially irresilient convolutions of refractory metal wire screwed on the external surface of said first metal convolution and abutting against said intermediate leaf.

6. A heat shield pack comprising: at least three concentrically disposed refractory metal heat shield leaves, means forming at least three apertures disposed on the intermediate of said heat shield leaves, means disposed and attached in the apertures of said intermediate leaf for separating it from the other two of said leaves, the distal ends of said separating means abutting against the other two of said leaves; a bottom closure of at least three heat shield discs of a refractory metal of equal diameter adapted to fit into the opening in one end of the concentrically formed leaves and to close off the lower end of said pack.

7. A high temperature furnace comprising: an outer tank, a cold wall adjacent the interior of said outer tank, at least three concentric open-ended refractory metal heat shield leaves, heater means disposed within said heat shield leaves; at least three apertures disposed in the intermediate heat shield leaf; means for separating the outer and inner heat shield leaves from the intermediate leaf, said means comprising a substantially irresilient convolution of a refractory metal wire extending through said apertures and on both sides of said intermediate leaf; a pair of substantially irresilient convolutions of refractory metal screwed on the external surfaces of each of said convolution means and abutting against said intermediate leaf, a lower closure of at least three spaced-apart refractory metal discs of equal diameter, said lower closure adapted to fit in the lower opening of said concentric leaves; a cover plate of at least three spaced apart refractory discs, at least one of said discs having a slightly smaller diameter than the other said discs, said cover plate fitting on the top opening of said concentric leaves, the smaller of the discs of said cover plate fitting into the top opening of said concentric leaves, thereby establishing an area completely enclosed by refractory metal heat shield plates.

8. A high temperature furnace comprising: an outer tank, a cold wall adjacent to the interior of said outer tank, at least three concentric open-ended refractory metal heat shield leaves, said concentric leaves positioned Within said cold Wall with one open end at the top and the other end at the bottom; means disposed upon and attached the intermediate leaf for separating the two outer leaves therefrom said means extending through said intermediate leaf and abutting against said two outer leaves but not attached thereto; a lower closure of at least three spaced-apart refractory metal discs of equal diameter, said lower closure adapted to fit in the lower opening of said concentric leaves, means forming upstanding supports disposed through said discs; 21. hearth plate disposed upon said support means; a refractory metal heating element positioned on said hearth plate within said concentric heat shield leaves, a coverplate of at least three spaced-apart refractory discs, one of said discs having a slightly smaller diameter than the other said discs, said coverplate fitting on the top opening of said concentric leaves, the smaller of the discs of said coverplate fitting into the top opening of said concentric leaves, to establish an area completely enclosed by refractory metal heat shield material.

9. A high temperature furnace comprising at least: a first outer leaf, a second intermediate leaf and a third inner leaf, said leaves being concentrically disposed and formed from a refractory metal; heater means disposed within said heat shield leaves; at least three aperture means disposed on said second intermediate heat shield leaf; means disposed and attached to the intermediate leaf in each of said apertures for separating said second intermediate leaf from said first outer leaf and said third inner leaf, the distal ends of each of said separating means abutting against said first outer leaf and said third inner leaf.

10. A high temperature furnace comprising at least: a first outer leaf, a second intermediate leaf and a third inner leaf, said leaves being concentrically disposed and formed from refractory metal loosely overlapped at their extremities; heater means disposed within said heat shield leaves; at least three aperture means disposed on said second intermediate heat shield leaf; means disposed and attached to the intermediate leaf in each of said apertures for separating said intermediate leaf from said first outer leaf and said third inner leaf, the distal ends of each of said separating means abutting against said first outer leaf and said third inner leaf.

UNITED STATES PATENTS References Cited 1,540,401 6/1925 Kelly et al. 219-406 2,404,060 7/1946 Hall et a]. 13-20 2,476,916 7/1949 Rose et a1 13-31 2,980,820 4/1961 Brundige et al. 313-279 3,033,547 5/1962 Baker et al. 263-40 3,124,634 3/1964 Western et al 13-31 3,170,018 2/1965 Lewis 13-31 3,185,460 5/1965 Mescher et a1 263-40 3,274,374 9/1966 Matheson et al 219-426 3,281,751 10/ 1966 Blair 339-17 FOREIGN PATENTS 565,961 11/1958 Canada. 861,257 2/1961 Great Britain.

RICHARD M. WOOD, Primary Examiner. V. Y. MAYEWSKY, Assistant Examiner. 

9. A HIGH TEMPERATURE FURNACE COMPRISING AT LEAST: A FIRST OUTER LEAF, A SECOND INTERMEDIATE LEAF AND A THIRD INNER LEAD, SAID LEAVES BEING CONCENTRICALLY DISPOSED AND FORMED FROM A REFRACTORY METAL; HEATER MEANS DISPOSED WITHIN SAID HEAT SHIELD LEAVES; AT LEAST THREE APERTURE MEANS DISPOSED ON SAID SECOND INTERMEDIATE HEAT SHIELD LEAF; MEANS DISPOSED ON SAID SECOND INTERMEDIATE HEAT SHIELD IN EACH OF SAID APERTURES FOR SEPARATING SAID SECOND INTERMEDIATE LEAF FROM SAID FIRST OUTER LEAF AND SAID THIRD INNER LEAF, THE DISTAL ENDS OF EACH OF SAID SEPARATING MEANS ABUTTING AGAINST SAID FIRST OUTER LEAF AND SAID THIRD INNER LEAF. 